The invention is directed to a thermal fuse for fixing on a circuit substrate in the form of a spring clip which comprises two contact locations, whereof at least one is a solder location for connection to corresponding circuit contacts of the substrate as well as at least one elastic spring arm as connecting section between the two contact locations. The invention is also directed to a method for the activation of such a thermal fuse.
Such fuses serve the purpose of protecting circuit parts against thermal overload and can be utilized in any desired circuits, for instance on printed circuit boards. The preferred area of employment of the thermal fuse of the invention, however, are film circuits.
In general, thermal fuses of the species initially cited are variously known and for various employments, for example from DE-B-15 15 624. In the fuse shown therein, the spring arm is pre-stressed into its working position when the fuse is built in. It must thus be retained in the pre-stressed position with a special device during soldering and until the soldered connection has cooled. Particularly given film circuits, this requires complicated manipulation and complicated devices.
In order to avoid soldering under tension, it has likewise already been proposed (DE-A-38 25 897 and DE-A-39 30 819) to support the spring arms of a U-shaped fuse clip in their prestressed position with applied support elements. No clamp or retainer devices are thus required during soldering; the support elements, however, must be removed or bent off after soldering in order to allow the tension of the spring arms to take effect. An object of the present invention is to enable an even simpler fashioning of a thermal fuse wherein neither a pre-stress mount during soldering nor a separate support element at the spring arms themselves are required.